![crossover symmetry crossover symmetry](https://i2.wp.com/www.intrepidpdx.com/wp-content/uploads/2015/08/FullSizeRender-2-e1440732959142.jpg)
The energy of the adjacent levels is so close together that they can be considered as a continuum, an energy band. Since the number of atoms in a macroscopic piece of solid is a very large number (N~10 22) the number of orbitals is very large and thus they are very closely spaced in energy (of the order of 10 −22 eV). Each discrete energy level splits into N levels, each with a different energy. Similarly, if a large number N of identical atoms come together to form a solid, such as a crystal lattice, the atoms' atomic orbitals overlap with the nearby orbitals. So if two identical atoms combine to form a diatomic molecule, each atomic orbital splits into two molecular orbitals of different energy. When two or more atoms join together to form a molecule, their atomic orbitals overlap and hybridize. The electrons of a single, isolated atom occupy atomic orbitals each of which has a discrete energy level. Decreasing the inter-atomic spacing even more (e.g., under a high pressure) further modifies the band structure.Īnimation of band formation and how electrons fill them in a metal and an insulator At the actual diamond crystal cell size (denoted by a), two bands are formed, called the valence and conduction bands, separated by a 5.5 eV band gap. Since N is a very large number in a macroscopic sized crystal, the adjacent levels are energetically close together, effectively forming a continuous energy band. The orbitals hybridize, and each atomic level splits into N levels with different energies, where N is the number of atoms. However, when the atoms come closer (left side), their electron orbitals begin to spatially overlap. When far apart (right side of graph) all the atoms have discrete valence orbitals p and s with the same energies. The right graph shows the energy levels as a function of the spacing between atoms. A hypothetical example of a large number of carbon atoms being brought together to form a diamond crystal, demonstrating formation of the electronic band structure.